Hexadecadehydrodibenzo[20]-, tetracosadehydrotribenzo[30]-, and dotriacontadehydrotetrabenzo[40]annulenes: Syntheses, characterizations, electronic properties, and self-associations

Article abstract of DOI:10.1021/jo401200m

Hexadecadehydrodibenzo[20]-, tetracosadehydrotribenzo[30]-, and dotriacontadehydrotetrabenzo[40]annulene derivatives ([20]-, [30]-, and [40]DBAs) possessing tetrayne linkages were synthesized. X-ray diffraction analysis demonstrated that the molecules of

Full text of DOI:10.1021/jo401200m

Article
pubs.acs.org/joc
Hexadecadehydrodibenzo[20]‑, Tetracosadehydrotribenzo[30]‑, and
Dotriacontadehydrotetrabenzo[40]annulenes: Syntheses,
Characterizations, Electronic Properties, and Self-Associations
Shin-ichiro Kato, Nobutaka Takahashi, and Yosuke Nakamura*
Division of Molecular Science, Faculty of Science and Technology, Gunma University, 1-5-1 Tenjin-cho, Kiryu, Gunma 376-8515,
Japan
S
* Supporting Information
ABSTRACT: Hexadecadehydrodibenzo[20]-, tetracosadehy-
drotribenzo[30]-, and dotriacontadehydrotetrabenzo[40]-
annulene derivatives ([20]-, [30]-, and [40]DBAs) possessing
tetrayne linkages were synthesized. X-ray diffraction analysis
demonstrated that the molecules of [30]DBA and p-xylene
form a 2D sheetlike structure. Planar [20]- and [30]DBAs
show significantly weak or almost no tropicity. The extension
of the acetylenic linkages from a diyne to a tetrayne unit
narrows HOMO−LUMO gaps. The self-association behavior
of [30]DBA in solution resulting from effective π−π stacking interactions was observed.
z o [ 2 0 ] - , t e t r a c o s a d e h y d r o t r i b e n z o [ 3 0 ] - , a n d
dotriacontadehydrotetrabenzo[40]annulene derivatives 3−5
possessing tetrayne linkages. By comparing the properties of
3−5 with those of [12]DBA 1b and [18]DBA 2b, we focused
on the elucidation of the relationship between the ring size and
the properties in the present DBA systems.
INTRODUCTION
■
Acetylenic macrocycles, particularly dehydro[n]annulenes
([n]DAs) and dehydrobenzo[n]annulenes ([n]DBAs) in
which n denotes the number of π electrons in the cyclic
pathway, have received long-lasting attention in not only the
basic aspect of aromaticity/antiaromaticity (namely, the
tropicity of cyclic π-conjugated systems)1 but also materials
science because of their particularly interesting optoelectronic
and self-assembling properties.2 Because the Cu-mediated
homocoupling reactions of ene-diynes or diethynylbenzenes,
which are available with relative ease, have been well
established, a variety of [n]DAs and [n]DBAs that consist of
alkene or benzene moieties, respectively, and diyne linkages at
the unsaturated bond were synthesized, including [12]DBA
1a,3 [18]DBA 2a,4 and their derivatives.2 Moreover, advances
in the field of Pd-catalyzed alkyne cross-coupling reactions have
brought about the synthesis of related DBAs with more
sophisticated functionality and the construction of larger and
more complex DBA systems.5
RESULTS AND DISCUSSION
■
Synthesis and Structures. The synthesis of DBAs 3−5 is
outlined in Scheme 1. Compound 6 was converted into
a
Scheme 1. Synthesis of [20]-, [30]-, and [40]DBAs 3−5
The incorporation of oligoyne linkages that are longer than
diyne linkages into DA and DBA systems would allow us to
obtain valuable insight into relevant structure−property
relationships, namely, the effects of the ring expansion on the
stability, tropicity, and electronic properties. However,
examples of DAs and DBAs possessing oligoyne linkages are
quite limited to date, and a summary of those in particular
resulting from the groups of Haley,6 Tobe,7 and Diederich8 is
included in Figure S1 in the Supporting Information. One of
the reasons for the lack of [n]DAs and [n]DBAs possessing
oligoyne linkages may be that acetylenic compounds become
unstable with an increasing number of conjugated CCC
bonds.9,10 We describe herein the syntheses, characterizations,
and properties of hitherto unknown hexadecadehydrodiben-
a
Reagents and conditions: (a) K2CO3, THF/MeOH (1:1), and rt. (b)
AgNO3, NBS, THF/MeOH (1:1), and rt. (c) CuCl, NH2OH·HCl, n-
BuNH2, TMSA, CH2Cl2/H2O (7:5), and 0 °C. (d) CuCl, TMEDA,
acetone, and −5 °C to rt. (e) [PdCl2(PPh3)2], CuI, p-benzoquinone,
THF/Et3N (1:2), and rt. TMSA = trimethylsilylacetylene. TMEDA =
N,N,N′,N′-tetramethylethylenediamine.
Received: June 8, 2013
© XXXX American Chemical Society
A
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deformed from linearity. The bending angles of the CCC
bonds in 3′ are 170.3−175.2°, whereas those in 1′ are 164.1−
167.5°; thus, the strain in CCC bonds in 3′ is predicted to
be released in comparison to that of 1′. The evidence for the
moderate strain in the CCC bonds of 3 is manifested by
the downfield shifts of the 13C NMR peaks of the sp carbons by
ca. 4 to 5 ppm for 3 compared to 4. Nevertheless, 3 shows
drastically reduced stability as compared to 1. Although the
reason for this finding is unclear at present, a similar severe
instability in cyclic alkyl tetraynes was reported by Tykwinski
and co-workers.14
Single crystals of 4 suitable for X-ray diffraction analysis were
obtained by recrystallization from a p-xylene solution as a
clathrate, with p-xylene having a 2:5 stoichiometry (Figure S2).
The CCC bond angles are 176.5−179.8°, and the
deviation from the mean plane composed of the benzene
moieties and tetrayne linkages is at most 0.205 Å. In the crystal
lattice, the large cavity of 4 is occupied with a p-xylene molecule
or the butoxy chain of the neighboring molecule. Interestingly,
the molecules of 4 and p-xylene form a 2D sheetlike structure
in which the [30]DBA cores roughly align within the plane
(Figure 1).15
bromoalkyne 7 via desilylation with K2CO3 followed by silver-
catalyzed bromination (52% in two steps). The Cadiot−
Chodkiewicz coupling of 7 with trimethylsilylacetylene
(TMSA) provided silyl-protected bisbutadiynyl arene 8
(28%). Desilylation of 8 with K2CO3 afforded the free alkyne
that showed only limited stability in its neat form, which was
rapidly placed under the Hay coupling condition in acetone.
The careful separation of the crude mixture obtained in the
macrocyclization afforded [20]DBA 3 and [30]DBA 4 (5% in
two steps). The yield of 3 could not be determined because 3
could be handled only in solution; a neat sample rapidly
polymerized to furnish black, intractable materials. The Pd-
catalyzed coupling reaction was also investigated, and [40]DBA
5 (6%) and 4 (7%) were isolated. The low yields from the
macrocyclization are probably due to the decomposition of the
free alkyne during the reactions and/or the formation of
oligomeric or polymeric products. Compounds 3−5 were
undoubtedly identified by MS (FAB or MALDI−TOF) analysis
together with their highly symmetric NMR spectra as described
below. DBAs 4 and 5 showed higher stability than 3 and could
be stored in the solid state at −15 °C for over a year. At room
temperature, the solid sample of [30]DBA 4 gradually
decomposed within a few months. However, [40]DBA 5 did
not show any sign of decomposition when kept in the solid
state for over a year. DBAs 1b and 2b were synthesized
according to a literature procedure.11,12
Figure 1. Packing structure of (DBA 4)2·(p-xylene)5.
1H NMR Spectra and NICS Calculations. DBAs 3−5
displayed very simple 1H NMR spectra; thus, one singlet signal
for aromatic protons was observed (Figures S17 and S18).
Planar [20]- and [30]DBAs 3 and 4 are formally antiaromatic
and aromatic, respectively. The change in resonance (Δδ) of
aromatic protons is a good indicator of the elucidation of
tropicity. The signal of the aromatic protons for 3 is upfield
shifted by Δδ = 0.28 ppm with respect to the signal for acyclic
8. The signal for 4 is only slightly downfield shifted by Δδ =
0.05 ppm, which is almost comparable to the shift (Δδ = 0.02
ppm) for nonplanar, apparently nonaromatic 5. The observed
chemical shift changes from acyclic 8 to 3 and 4 are apparently
small as compared to those from 6 to 1b and 2b, respectively;
the Δδ values are 0.51 ppm for 1b and 0.20 ppm for 2b with
respect to 6. This finding indicates that the tropicity of 3 and 4
substantially decreases as compared to corresponding 1b and
2b owing to the expansion of the dehydroannulene ring.
Vollhardt and Matzger first reported the attenuating effect of
the increase in the size of DBA rings on the NICS values.3b,16
Indeed, the NICS(0) (and NICS(1)) values of 3′ calculated at
the GIAO/HF/6-31G*//B3LYP/6-31G* level are +1.14
(+1.07), which are only ca. 30% of those of 1′ (+3.84
We calculated the molecular structures of [20]-, [30]-, and
[40]DBAs 3′−5′ together with [12]DBA 1′ and [18]DBA 2′,
in which the butoxy groups in 1−5 were replaced with methoxy
groups, at the B3LYP/6-31G* level of theory.13 Optimized
structures 1′−4′ are planar (D2h symmetry for 1′ and 3′, D3h
symmetry for 2′ and 4′). The structure of 5′ was calculated to
be a nonplanar D2d-symmetric structure (Figure S9). Unlike 2′,
4′, and 5′, the CCC bonds in 1′ and 3′ are apparently
B
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(+3.70)); the NICS(0) (and NICS(1)) values for parent
octadehydro[12]annulene are calculated to be +9.20 (+8.10).
The NICS(0) (and NICS(1)) of 4′ are calculated to be +0.14
(+0.13), which are obviously paradoxical values for compounds
with macrocyclic diatropicity. Thus, it is considered that the
paratropicity of 3 is significantly weak and the diatropicity of 4
is negligible.
Table 1. Oxidation and Reduction Potentials of DBAs 1b,
2b, 3, 4, and 5 by CV in o-Dichlorobenzene and
a
Theoretically Calculated HOMO and LUMO Levels and
b
their Gaps (ΔEcalcd
)
ox
red
Eonset
Eonset
ΔEredox HOMO LUMO
ΔEcalcd
c
(Epa) (V)
(Epc) (V)
(V)
(eV)
(eV)
(eV)
1b
+0.63
−1.99
(−2.16)
(−2.51)
2.62
−5.08
−2.29
2.79
Electronic and Electrochemical Properties. In the
electronic absorption spectra (Figure 2), the red shifts of the
d
e
(+0.78)
d
f
(+1.21)
2b
3
+0.82
−2.17
(−2.43)
−1.70
(−1.81)
2.99
2.52
−5.24
−5.28
−1.96
−2.84
3.28
2.44
f
f
(+0.96)
+0.82
d
e
(+0.92)
d
f
(+1.14)
(−1.99)
4
5
+0.92
−1.76
(−1.99)
−1.81
2.68
2.76
−5.40
−5.72
−2.66
−2.79
2.74
2.93
f
f
(+1.03)
g
+0.95
f
(+1.05)
a
0.1 mol L−1 n-Bu4NPF6. All potentials are given versus the Fc+/Fc
b
couple used as an external standard. Scan rate: 100 mV s−1. B3LYP/
6-31+G**//B3LYP/6-31G* for 1′−5′, where the butoxy groups in
c
1b, 2b, 3, 4, and 5 are replaced with methoxy groups. The
electrochemical gap, ΔEredox, is defined as the potential difference
d
e
between Eonsetox and Eonsetred. Reversible wave. Quasi-reversible wave.
f
g
Irreversible wave. Unresolved wave.
to those of 1b and 2b, respectively. The electrochemical
HOMO−LUMO gaps become apparently small from 5 and 4
to 3, as expected from the absorption spectra. These trends are
well reproduced by the calculations; the ΔEredox values for 1b,
2b, and 3−5 match the calculated gaps (ΔEcalcd) for
corresponding 1′−5′.
Figure 2. UV−vis spectra of DBAs 1b and 3 (a) and 2b, 4, and 5 (b)
in CHCl3 at 298 K. The data for 3 are plotted with arbitrary intensity
because of its instability in the solid state.
1
Self-Association. Unexpectedly, the H NMR spectra of 4
in CDCl3 showed subtle but distinctive upfield shifts of the
aromatic protons upon increasing the concentration (Figure
3a). This indicates the occurrence of self-association in solution
longest absorption maxima (λmax) are observed in 3 and 4
compared with 1b and 2b, respectively, which are attributed to
the extension of π conjugation as a result of the extension of the
acetylenic linkages (472 nm (1b), 396 nm (2b), 490 nm (3),
and 451 nm (4)).17,18 Notably, the λmax and absorption onsets
are red shifted from 5 and 4 to 3 in spite of 3 having the
smallest ring size. Considering that the paratropicity of 3 is
significantly weak and the conjugation pathway of 3 is shorter
than that of 4 and 5, the smaller HOMO−LUMO gap of 3
compared to 4 and 5 may derive from the strained acetylenic
linkages in 3.19 The blue-shifted λmax (418 nm) and absorption
onset in 5 relative to 3 and 4 is readily explained by the
considerable nonplanarity of 5, which should suppress the π
conjugation to some extent in the macrocyclic framework
composed of the benzene moieties and tetrayne linkages. DBAs
1b and 3−5 are nonfluorescent, whereas 2b is fluorescent with
an absolute fluorescence quantum yield of 0.36 in CHCl3.
To gain insight into the frontier orbital energy of DBAs 3−5
as well as 1b and 2b, CV analysis in o-dichlorobenzene was
conducted (Table 1). All of the DBAs displayed amphoteric
behavior within the available potential window (Figures S4−
S8). Both the oxidation onsets (Eonsetox) and reduction onsets
(Eonsetred) for 3 and 4 are positively shifted as compared to
those for 1b and 2b, respectively, reflecting the stronger
electron-withdrawing ability of a tetrayne unit compared to that
of a diyne unit.20 The Eonsetred values are more positively shifted
Figure 3. (a) 1H NMR spectra of 4 in various concentrations of
CDCl3 at 298 K. (b) Nonlinear curve-fitting plots of the concentration
dependence of the chemical shifts for aromatic protons of 4.
by π−π stacking interactions. The diffusion coefficients, D, for 4
were almost independent of the concentrations on the basis of
the diffusion NMR experiments, suggesting that a monomer−
dimer equilibrium predominantly exists.21 A plot of the
chemical shifts of the aromatic protons as a function of
concentration was fitted to a curve for the monomer−dimer
model (Figure 3b)22 and yielded the self-association constant
(Ka) of 4 1 L mol−1. In contrast to 4, the resonance for the
aromatic protons in 2b was independent of the concentration
in CDCl3. These results demonstrate that the extension of the
acetylenic linkages from 2b to 4 enhances the self-association
ability. To investigate the effect of solvent polarity on the self-
ox
than the Eonset values; hence, 3 and 4 have smaller potential
ox
red
differences (ΔEredox) between the Eonset and Eonset values
(namely, the electrochemical HOMO−LUMO gaps) compared
C
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acetone (10 mL) were added N-bromosuccinimide (784 mg, 4.40
mmol) and AgNO3 (96 mg, 0.57 mmol). After the mixture was stirred
at room temperature for 6 h, the suspension was evaporated under
reduced pressure. The residue was suspended with hexane and filtered,
and the filtrate was evaporated under reduced pressure. The residue
was purified by silica gel column chromatography (hexane/CH2Cl2,
10:1) to afford 7 (430 mg, 1.00 mmol, 52%) as a red solid. mp 64−66
°C. 1H NMR (CDCl3, 300 MHz) δ 0.97 (t, 6H, J = 7.4 Hz), 1.48 (tq,
4H, J = 7.4, 7.2 Hz), 1.78 (tt, 4H, J = 7.2, 6.8 Hz), 3.95 (t, 4H, J = 6.8
Hz), 6.86 (s, 2H). 13C NMR (CDCl3, 75 MHz) δ 13.8, 19.2, 31.1,
51.9, 68.8, 78.6, 116.1, 118.4, 149.2. UV−vis (CH2Cl2) λmax = 290 nm.
MALDI−TOF MS (Dith, positive) [M + Na]+ 451.00. Anal. Calcd for
C18H20Br2O2: C, 50.49; H, 4.71. Found: C, 50.03; H, 4.71.
association of 4, we performed the NMR experiments in the
CDCl3/CD3CN solvent system. The Ka values in CDCl3/
CD3CN ratios of 2:1 and 1:1 were 56 5 and 112 45 L
mol−1, respectively (Figure S16 in the Supporting Information),
which indicate that the self-association is enhanced by the
solvophobic effects in the mixed-solvent system.
To examine the electronic effect of the acetylenic linkages on
the self-association, we calculated the electrostatic-potential
surfaces (ESPs) and molecular electrostatic potentials (MEPs)
of 2′ and 4′ at the B3LYP/6-31+G**//B3LYP/6-31G* level
(Figure 4). The MEPs at 2 Å above the center of the benzene
Preparation of 8. To a suspension of CuCl (50 mg, 0.5 mmol)
and n-BuNH2 (3.6 mL, 35 mmol) in water (5 mL) and CH2Cl2 (5
mL) was added NH2OH·HCl (5 mg, 0.1 mmol) at 0 °C. A solution of
7 (430 mg, 1.00 mmol) and trimethylsilylacetylene (0.42 mL, 3.00
mmol) in CH2Cl2 (2 mL) was added dropwise to the mixture at 0 °C.
After the resulting mixture was stirred at 0 °C for 40 min, aqueous
NH4Cl (10%, 30 mL) was added. The organic phase was successively
washed with aqueous NH4Cl (10%, 30 mL) and water (20 mL × 2),
dried over anhydrous MgSO4, and evaporated under reduced pressure.
The residue was purified by silica gel column chromatography
(hexane/CH2Cl2, 5:1) and recycling GPC (CHCl3) to afford 8 (130
Figure 4. Electrostatic-potential surfaces and values of the molecular
electrostatic potentials (MEPs; the calculated position of the MEP is 2
Å above the center of the benzene ring) of 2′ (a) and 4′ (b) at the
level of B3LYP/6-31+G**//B3LYP/6-31G*. The potentials are
drawn in the same color scale, with red indicating more-negative
electrostatic potentials and blue, more-positive potentials.
1
mg, 0.28 mmol, 28%) as yellow oil. H NMR (CDCl3, 300 MHz) δ
0.24 (s, 18H), 0.97 (t, 6H, J = 7.4 Hz), 1.43−1.51 (m, 4H), 1.79 (tt,
4H, J = 6.8, 6.8 Hz), 3.96 (t, 4H, J = 6.8 Hz), 6.90 (s, 2H). 13C NMR
(CDCl3, 125 MHz) δ −0.2, 13.9, 19.2, 31.0, 68.9, 75.2, 76.8, 88.2, 91.8,
116.9, 117.9, 149.9. UV−vis (CHCl3) λmax (rel. int.) = 255 (0.31), 270
(0.60), 286 (1.00), 329 (0.35), 352 (0.36) nm. MALDI−TOF MS
(Dith, positive) (M+) 462.58. Anal. Calcd for C28H38O2Si2·0.04
CHCl3: C, 72.03; H, 8.20. Found: C, 71.78; H, 7.85.
rings are −8.8 and −4.0 kcal mol−1 for 2′ and 4′, respectively,
which clearly indicates a less-negative character for the benzene
rings of 4 than 2b. It has been widely accepted that electron-
withdrawing aromatic rings favor effective π−π stacking
interactions.23 Again, it was pointed out by Tobe and co-
workers that arylene−butadiynylene macrocycles possess a
higher self-association ability than arylene−ethynylene macro-
cyles because of the strong electron-withdrawing effect of the
butadiyne units in the former.24 Therefore, it is reasonable to
conclude that the tetrayne linkages in 4 promote π−π stacking
interactions effectively owing to their strong electron-with-
drawing effect.
Preparation of DBAs 3 and 4 (Cu-Mediated Method). A
mixture of 8 (656 mg, 1.42 mmol) and K2CO3 (392 mg, 2.84 mmol)
in THF/MeOH (1:1, 10 mL) was stirred at room temperature for 1 h.
After the mixture was diluted with acetone (20 mL), the insoluble
material was removed by filtration, and the filtrate was evaporated
under reduced pressure. The residue was purified by silica gel column
chromatography (acetone) to give desilylated alkyne, which was used
in the next coupling reaction without further purification because of
the instability. To a mixture of the desilylated alkyne and TMEDA (1.0
mL, 7.10 mmol) in acetone (250 mL) was added CuCl (700 mg, 7.10
mmol) at −5 °C, and the resulting mixture was stirred at room
temperature for 22 h. The mixture was filtered through a bed of silica
gel, and the filtrate was evaporated under reduced pressure to ca. 1 mL.
The mixture was purified by silica gel column chromatography
(hexane/toluene, 1:1) to afford unstable [20]DBA 3 and [30]DBA 4
(22 mg, 0.023 mmol, 5%) as yellow solids. [20]DBA 3 decomposed
upon concentration to give an insoluble black material. A dilute
CONCLUSIONS
■
We have synthesized hitherto unknown [20]-, [30]-, and
[40]DBAs 3−5 possessing tetrayne linkages. The unique 2D
sheetlike network of (DBA 4)2·(p-xylene)5 in the solid state
was revealed. The expansion of the DBA cores by extension of
the acetylenic linkages from a diyne to a tetrayne unit
significantly decreases tropicity; thus, the paratropicity of 3
should be extremely weak, and the diatropicity of 4 should be
negligible. The tetrayne linkages are responsible for small
HOMO−LUMO gaps compared to those with diyne linkages.
The effective self-association properties of 4 in solution suggest
that tetrayne linkages facilitate π−π stacking interactions.
Further exploration of the synthesis of novel dehydroannulenes
having tetrayne linkages is currently underway in our group.
1
solution of 3 can be stored for over a year at −15 °C. 3: H NMR
(CDCl3, 600 MHz) δ 0.96 (t, 12H, J = 7.3 Hz), 1.45 (tq, 8H, J = 7.3,
7.3 Hz), 1.76 (tt, 8H, J = 7.3, 6.9 Hz), 3.91 (t, 8H, 6.9 Hz), 6.62 (s,
4H). 13C NMR (CDCl3, 150 MHz) δ 13.9, 19.2, 31.0, 67.7, 69.0, 70.8,
80.3, 82.2, 114.0, 122.0, 150.5. UV−vis (CHCl3) λmax (rel. int.) = 490
(0.02), 447 (0.03), 383 (0.27), 356 (0.24), 332 (0.16), 309 (0.22), 282
(1.00) nm. HR−FAB MS (NBA, positive) m/z (M+) calcd for
+
1
C44H40O4 , 632.2927; found, 632.2927. 4: mp 155 °C (decomp.). H
NMR (CDCl3, 2.53 × 10−3 L−1 mol, 500 MHz) δ 0.98 (t, 18H, J = 7.5
Hz), 1.50 (tq, 12H, J = 7.5, 7.3 Hz), 1.81 (tt, 12H, J = 7.3, 6.8 Hz),
4.00 (t, 12H, J = 6.8 Hz), 6.95 (s, 6H). 13C NMR (CDCl3, 125 MHz)
δ 13.9, 19.2, 31.0, 64.4, 68.93, 69.04, 75.7, 77.6, 116.5, 118.3, 150.4.
UV−vis (CHCl3) λmax (ε) = 451 (62 200), 411 (98 100), 380 (62
600), 347 (41 200), 284 (277 300) nm. HR−FAB MS (NBA, positive)
EXPERIMENTAL SECTION
■
+
m/z (M+) calcd for C66H60O6 , 948.4390; found, 948.4380.
Preparation of 7. To a solution of 6 (800 mg, 1.93 mmol) in
THF/MeOH (1:1, 10 mL) was added K2CO3 (528 mg, 3.82 mmol).
After the mixture was stirred at room temperature for 50 min, the
suspension was evaporated under reduced pressure. The residue was
purified by silica gel column chromatography (acetone) to give
desilylated diyne, which was used in the next reaction without further
purification because of the instability. To a solution of the diyne in
Preparation of DBAs 4 and 5 (Pd-Catalyzed Method).
Compound 8 (322 mg, 0.88 mmol) was desilylated according to the
same procedure used for the preparation of DBAs 3 and 4. A solution
of the desilylated alkyne in Et3N/THF (1:2, 90 mL) was bubbled with
argon with stirring for 30 min. [PdCl2(PPh3)2] (62 mg, 0.088 mmol),
CuI (34 mg, 0.176 mmol), and p-benzoquinone (85 mg, 0.79 mmol)
D
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Article
were added to the solution, and the resulting mixture was stirred at
room temperature for 16 h under argon atmosphere. The mixture was
filtered through a bed of silica gel, and the filtrate was evaporated
under reduced pressure. The residue was subjected to silica gel column
chromatography (CHCl3). The collected material was suspended with
CH2Cl2, and the insoluble material was collected by filtration, which
was further washed with CH2Cl2 to afford [40]DBA 5 (16 mg, 0.013
mmol, 6%) as a yellow solid. An analytical sample was obtained by
reprecipitation from CHCl3/hexane. The filtrate was concentrated
under reduced pressure. The residue was further purified by recycling
GPC (CHCl3) to afford [30]DBA 4 (18 mg, 0.019 mmol, 7%). 5: mp
(6) (a) Wan, W. B.; Kimball, D. B.; Haley, M. M. Tetrahedron Lett.
1998, 39, 6795. (b) Bell, M. L.; Chiechi, R. C.; Johnson, C. A.;
Kimball, D. B.; Matzger, A. J.; Wan, W. B.; Weakley, T. J. R.; Haley, M.
M. Tetrahedron 2001, 57, 3507. (c) Wan, W. B.; Chiechi, R. C.;
Weakley, T. J. R.; Haley, M. M. Eur. J. Org. Chem. 2001, 3485.
(7) (a) Tobe, Y.; Ohki, I.; Sonoda, M.; Niino, H.; Sato, T.;
Wakabayashi, T. J. Am. Chem. Soc. 2003, 125, 5614. (b) Hisaki, I.; Eda,
T.; Sonoda, M.; Niino, H.; Sato, T.; Wakabayashi, T.; Tobe, Y. J. Org.
Chem. 2005, 70, 1853.
(8) Kivala, M.; Mitzel, F.; Boudon, C.; Gisselbrecht, J.-P.; Seiler, P.;
Gross, M.; Diederich, F. Chem.Asian J. 2006, 1, 479.
1
148 °C (decomp.). H NMR (CDCl3, 600 MHz) δ 0.97 (t, 24H, J =
(9) (a) Wegner, G. Macromol. Chem. 1972, 154, 35. (b) Wegner, G.
Angew. Chem., Int. Ed. Engl. 1981, 26, 361.
7.3 Hz), 1.41−1.52 (m, 16H), 1.80 (tt, 16H, J = 6.4, 6.4 Hz), 3.99 (t,
16H, J = 6.4 Hz), 6.92 (s, 8H). 13C NMR (CDCl3, 125 MHz) δ 13.9,
19.2, 31.0, 64.5, 68.9, 69.1, 76.0, 77.7, 116.8, 118.3, 150.5. UV−vis
(CHCl3) λmax (ε) = 418 (48 400), 397 (68 200), 364 (99 700), 343
(128 300), 298 (259 100) nm. MALDI−TOF MS (SA, positive) [M +
H]+ 1273.87. Anal. Calcd for C88H80O8·0.29 CHCl3: C, 81.55; H, 6.22.
Found: C, 81.55; H, 6.39. We were unable to obtain satisfactory
elemental analysis for this compound. This compound may tend to
contain solvent molecules in the solid state. We believe that the
(10) For selected examples of stable polyynes, see (a) Gibtner, T.;
Hampel, F.; Gisselbrecht, J.-P.; Hirsch, A. Chem.Eur. J. 2002, 8, 408.
(b) Zheng, Q.; Gladysz, J. A. J. Am. Chem. Soc. 2005, 127, 10508.
(c) Chalifoux, W. A.; Tykwinski, R. R. Nat. Chem. 2010, 2, 967.
(11) Tahara, K.; Johnson, C. A., II; Fujita, T.; Sonoda, M.; De
Schryver, F. C.; De Feyter, S.; Haley, M. M.; Tobe, Y. Langmuir 2007,
23, 10190.
(12) Kato, S.-i.; Takahashi, N.; Tanaka, H.; Kobayashi, A.; Yoshihara,
T.; Tobita, S.; Yamanobe, T.; Uehara, H.; Nakamura, Y.Chem.Eur. J.,
DOI: 10.1002/chem.201301262, in press.
(13) All calculations were carried out using Frisch, M. J.; Trucks, G.
W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.;
Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji,
H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.;
Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.;
Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao,
O.; Nakai, H.; Vreven, T.; Montgomery, Jr., J. A.; Peralta, J. E.;
Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin, K. N.;
Staroverov, V. N.; Keith, T.; Kobayashi, R.; Normand, J.; Raghavachari,
K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.;
Rega, N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.;
Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.;
Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.;
Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.;
Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, O.;
Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J.Gaussian 09,
revision B.01; Gaussian, Inc.: Wallingford, CT, 2010.
(14) Spantulescu, A.; Luu, T.; Zhao, Y.; McDonald, R.; Tykwinski, R.
R. Org. Lett. 2008, 10, 609.
(15) For discussion of the crystal packing, see the Supporting
Information (Figure S3).
(16) The NICS value has been successfully used as a measure of
tropicity. See von Rague Schleyer, P.; Maerker, C.; Dransfeld, A.; Jiao,
H.; van Eikema Hommes, N. J. R. J. Am. Chem. Soc. 1996, 118, 6317.
(17) The concentration of CHCl3 solution for 1b, 2b, 4, and 5 was
10−5−10−6 mol L−1. No deviation from the Lambert−Beer law was
observed for 4, indicating that the self-association of 4 is negligible
within the studied concentration range.
1
compound is pure on the basis of the H NMR spectrum.
ASSOCIATED CONTENT
* Supporting Information
■
S
General experimental methods, X-ray data (including a CIF
file), electrochemistry, theoretical data, self-association proper-
ties, and 1H and 13C NMR spectra of all new compounds. This
material is available free of charge via the Internet at http://
pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: nakamura@gunma-u.ac.jp. Tel: +81 277 30 1310. Fax:
+81 277 30 1314.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by a Grant-in-Aid for Scientific
Research from the Ministry of Education, Culture, Sports,
Science and Technology, Japan and the Japan Prize
Foundation. We thank Dr. Mikio Yamasaki (Rigaku) and Dr.
Akihiro Tsurusaki (Gunma University) for X-ray analysis, Dr.
Yoshihito Shiota (Kyushu University) for helpful suggestions
on the theoretical calculations, and Dr. Keisuke Tao and Prof.
Teruo Shinmyozu (Kyushu University) for MALDI−TOF MS
measurements.
(18) For the assignment of the longer-wavelength absorption in the
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dx.doi.org/10.1021/jo401200m | J. Org. Chem. XXXX, XXX, XXX−XXX